This section is from the book "Anatomy Of The Arteries Of The Human Body", by John Hatch Power. Also available from Amazon: Anatomy of the Arteries of the Human Body, with the Descriptive Anatomy of the Heart.
The Inferior External Articular Artery comes off a little lower down than the preceding. It crosses outwards beneath the external head of the gastrocnemius muscle, and then turns forwards between the external lateral ligament and convex margin of the external semi-lunar cartilage. At first this artery lies on the posterior surface of the popliteus muscle, it then crosses the muscle and afterwards lies at the lower margin of its tendon: finally it terminates in two branches, one of which ascends along the external margin of the patella, and anastomoses with the superior external articular artery; the other descends and divides into two branches, one of which sinks behind the ligamentum patellae, and is lost in the fat in this situation; the second anastomoses with the tibial recurrent.
The Muscular Branches have been divided into two sets, the superior and the inferior; the former are distributed to the muscles forming the upper boundaries of the popliteal space; the latter, called the sural arteries, are distributed to the heads of the gastrocnemii and plantaris muscles. The popliteal artery also gives off a small vessel which accompanies the posterior saphena vein.